EP0657590B1

EP0657590B1 - Automatic excavation control system for shovel type construction equipment

Info

Publication number: EP0657590B1
Application number: EP94309150A
Authority: EP
Inventors: Satoshi C/O Shin Caterpillar Fujii; Shoji C/O Shin Caterpillar Tozawa; Tomoaki C/O Shin Caterpillar Ono
Original assignee: Caterpillar Mitsubishi Ltd; Shin Caterpillar Mitsubishi Ltd
Current assignee: Caterpillar Japan Ltd; Caterpillar Mitsubishi Ltd
Priority date: 1993-12-09
Filing date: 1994-12-08
Publication date: 1998-07-08
Anticipated expiration: 2014-12-08
Also published as: CA2137631C; DE69411519D1; EP0657590A1; CA2137631A1; US5535532A; DE69411519T2; JPH07158105A

Description

Field of the Invention

The present invention relates to an excavator control apparatus for construction equipment of the type having a shovel such as a hydraulically operated shovel.

Description of the Related Art

In general, in some such shovel type construction equipment, the boom, arm, and bucket, which comprise the operation section, are successively rotatably connected to the equipment body, with the boom, arm and bucket each having connected thereto cylinders which expand and contract by lever operation. Digging with such equipment must be carried out by a very experienced operator because each of the cylinders must be operated separately. Since there are not enough experienced operators today, a shovel type construction equipment has been proposed in which each of the cylinders are automatically controlled to perform automatic digging. However, in such an equipment which carries out automatic digging so that the digging load remains constant, a large variation in digging depth may occur due to changes in the hardness of the ground to be dug or the presence of obstacles. This gives rise to the problem that digging with high precision cannot be achieved. In particular, when the ground is excavated beyond an intended depth, earth must be returned to ground, so that digging efficiency is considerably reduced. In addition, in correcting the variations in digging depth, the automatic digging control mode must be cancelled every time to operate the lever, which results in increased number of digging steps, thereby reducing digging efficiency.

WO-A-9102853 discloses an automatic excavation control system in which a number of different modes of operation are possible, for example: modes in which a particular part of the excavation equipment can be kept at a fixed orientation, modes in which excavation is limited to certain defined areas, a mode which monitors the forces on the driving cylinders and an automatic mode which in principle requires no human intervention once initiated. However, there is no disclosure of automatically switching between modes in accordance with pre-determined conditions.

In view of the above-described problems, the present invention is aimed at providing an excavator control apparatus for a shovel type construction equipment. According to the present invention, there is provided an excavator control apparatus for construction equipment of the type which has a movable boom, an arm pivotably coupled to the boom, a bucket carried by the arm, an operating section rotatably coupled to the equipment body, and operating cylinders for operating the boom, arm and bucket, said operating section comprising an automatic digging control section which allows automatic digging by controlling the operation of each of said cylinders, and being characterised by

digging load control means for detecting a digging load when a digging depth is shallower than a set digging depth during automatic digging and for generating operating commands for each of the cylinders so that the cylinders are operable to maintain said detected digging load at a set load;

bucket path control means for generating operating commands to each of the cylinders so that the cylinders are operated in such a way that the bucket is caused to follow a path, during automatic digging, which corresponds to set a path; and

control automatic switching means for automatically switching between a digging load control mode and a bucket path control mode in accordance with predetermined conditions.

The digging control section can comprise depth limiting means for correcting the operation commands to each of the cylinders so that the digging depth during automatic digging does not become less than a set depth value.

The digging control section can comprise operation command correcting means for correcting the operation command to each cylinder by lever operation during automatic digging.

Still further there can be provided control automatic switching means for automatically switching the mode from digging load control mode to the bucket path control mode when the digging depth has equalled a set depth.

Still further there can be provided control automatic switching means for automatically switching the mode from the bucket path control mode to the digging load control mode when a digging overload has occurred.

Still further there can be provided first control automatic switching means for automatically switching the mode from the digging load control mode to the bucket path control mode when the digging depth has equalled a set depth, and second control automatic switching means for automatically switching the mode from the bucket path control mode to the digging load control mode when a digging overload has occurred.

In a development of the invention, there is provided an excavator control apparatus for a shovel type construction equipment so constructed as having a boom, arm, and bucket, which comprise the operation section, successively rotatably connected to the equipment body, with the boom, arm and bucket each having connected thereto a cylinder or cylinders which expand and contract by lever operation, wherein an automatic digging control section of the apparatus, which allows automatic digging by controlling the expansion and contraction of the cylinders, incorporates digging load control means for generating operation commands to each of the cylinders to maintain the digging load during automatic digging at a set load, operation command correcting means for correcting the operation commands generated to each of the cylinders by lever operation during automatic digging, depth limiting means for correcting the operation commands generated to each of the cylinders to prevent the digging depth during automatic digging from becoming less than a set depth, and bucket path control means for generating operation commands to each of the cylinders to match the bucket path during automatic digging at a set path, first control automatic switching means for automatically switching the mode from digging load control mode to bucket path control mode when the digging depth has equaled a set depth, and second control automatic switching means for automatically switching the mode from the bucket path control mode to the digging load control mode.

The present invention, which is constructed as mentioned above, allows the operator to carry out digging operations very easily with high precision and efficiency.

The invention will be described now by way of example only, with particular reference to the accompanying drawings. In the drawings:

Fig. 1 is a perspective view of a hydraulic shovel-type apparatus;

Fig. 2 is a block diagram showing the overall construction of an excavator control apparatus;

Fig. 3 is a flow chart showing a digging load control mode;

Fig. 4 is a flow chart showing a bucket path control mode; and

Fig. 5 is a flow chart showing a combined control mode.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Next, an embodiment of the present invention will be described with reference to drawings.

Referring to Fig. 1, reference numeral 1 denotes a hydraulic shovel type construction equipment which is one example of a shovel type construction equipment. The hydraulic shovel 1 comprises a crawler moving section 2, a swinging section 3 which is swingably supported on the upper portion of the moving section 2, and an operation section 4 which is connected to the front end portion of the swinging section 3. Each of the aforementioned sections operates by hydraulic power of an engine (not shown) which is provided in the rear portion of the swinging section 3. Each of the sections are basically constructed as they are conventionally.

The swinging section 3 is supported on the upper portion of the moving section 2 by means of swing bearings (not shown). It swings by a hydraulic motor 5 which engages with the inner teeth of the swing bearings. The swinging position of the swinging section 3 is detected by a swinging position detecting sensor 6 and fed back to a control section 7 which will be described later.

The operation section 4 comprises a boom 8 which is connected to the front end portion of the swinging section 3 so as to be swingable in an upright plane, an arm 9 which is connected to the front end portion of the boom 8 such that it can swing to-and-fro, a bucket 10 which is connected to the front end portion of the arm 9 such that it can swing to-and-fro, boom cylinders 11 which vary the posture of the boom 8, an arm cylinder 12 which varies the posture of the arm 9, and a bucket cylinder 13 which varies the posture of the bucket 10. The

aforementioned cylinders

11, 12, and 13 each have an operating position and

speed detecting sensor

14, 15, and 16, respectively, which detect the operating position and speed to feed back the detected information to the control section 7.

Reference numeral 17 denotes a control valve which allows operation switching of each of the

cylinders

11, 12, and 13 and the aforementioned motor 5. Pilot-operated

electromagnetic valves

18, 19, 20, and 21 are each connected, respectively, to the control valve for the hydraulic motor 5 and each of the

cylinders

11, 12, and 13 each of which are provided therein. For this reason, the operating speed of the hydraulic motor 5 and each of the

cylinders

11, 12, and 13 can be freely controlled by a method which utilizes PWM to control the current of each of the

electromagnetic valves

18, 19, 20, and 21.

Reference numerals

22L and 22R denote a pair of operation levers on the left and right hand side of the operator's seat. The operating levers 22L and 22R allow the hydraulic motor to cause each of the

cylinders

11, 12, and 13 to move tiltably individually or together to the right or left, or backward or forward. The operation direction and the operation input of the cylinders are electrically detected and input to the control section 7.

The control section 7 is formed by a microcomputer which includes a CPU, ROM, and RAM. The control section 7 causes signals to be input by such component parts as: the aforementioned swinging position detecting sensor 6, the operating position and

speed detecting sensors

14, 15, and 16, and the operating levers 22L and 22R; a digging load detecting sensor 23 for detecting the digging load based on the pressure exerted by the arm cylinder 12; an automatic main switch 24 for switching automatic digging control mode ON and OFF; mode change-over switch 25 for switching automatic digging control modes (which include digging load control mode for executing only digging load control mode, bucket path control mode for executing only bucket path control mode, combined control mode for automatically switching the digging load control mode and the bucket path control mode); an automatic digging start (end) switch 26 for starting and ending the automatic digging control mode; a digging load setting element 27 for setting a standard load for the digging load control mode; a digging depth setting element 28 for setting a depth limit for digging load control mode and a standard depth for bucket path control mode; and an earth-moving position setting element 29 for setting the earth-moving position in automatic earth-moving control mode. Judging the input signals, the control section 7 causes operation signals to be output to the aforementioned

electromagnetic valves

18, 19, 20, 21, etc. In the control section 7, there has been previously stored control procedures for manual operation control, in which operation signals based on the operation of the

operating levers

22L and 22R in the operation section causes the operation of a corresponding hydraulic actuator (of hydraulic motor 5 or each of the

cylinders

11, 12, or 13 ) to be controlled. In addition there are previously stored procedures for automatic digging control (digging load control mode, bucket path control mode, and combined control mode) to be described later, as well as procedures for automatic earth-moving control in which the bucket 10 is moved from the place where digging is completed to a set earth-moving position to automatically remove earth. The automatic digging control mode has been selected among the various modes and will be described in detail below since it is considered the essence of the present invention.

The aforementioned automatic digging control mode is executed when the automatic digging start (end) switch 26 is switched (at the location where digging is started), while the automatic main switch 24 is turned on. On the other hand, the control mode is canceled, when the automatic digging control operation, itself, is completed, by re-operating the automatic digging start (end) switch 26, with the automatic main switch 24 switched off. The automatic digging control mode of the embodiment includes a digging load mode, a bucket path control mode, and a combined control mode. These modes can be alternatively executed by switching a mode change-over switch 25.

In the digging load control mode, a command is generated to expand the arm cylinder 12 and the bucket cylinder 13 for carrying out automatic digging. During automatic digging, the load detected by the digging load detecting sensor 23 and the load set by the digging load setting element 27 are constantly compared with each other. (In the embodiment, since a correction of a set value is based on an initial digging load, the corrected set load value is compared with the detected load value). At the same time, the upward and downward movement of the boom 8 can be controlled based on the compared results. When the detected load and the set load match (including neutral zone), signals are no longer sent to the boom cylinder 11. When the detected load is greater than a set load, a command is generated to the boom cylinder 11 for cylinder expansion to reduce the digging load. On the other hand, when the detected load is less than a set load, a command is generated to the boom cylinder 11 to contract the cylinder for increasing the digging load. Based on these three factors, very efficient automatic digging can be performed with a constant digging load. The digging load control mode is completed when the arm cylinder 12 or the bucket cylinder 13 has reached the end of its stroke.

In addition, in the digging load control mode, the control section constantly judges whether or not the operating

lever

22L or 22R has been operated during automatic digging. When it has been operated, the command values (electromagnetic valve current values) of the

cylinders

11, 12, and 13 are each adjusted depending on the lever operation input. That is, even during automatic digging, the operation of the operating

lever

22L or 22R allows the operation position and the operation speed of each of the

cylinders

11, 12, and 13 to be freely corrected.

Further, in the digging load control mode, the control section computes the current digging depth based on the detected values of the operation position and

speed detecting sensors

14, 15, and 16. At the same time, it constantly compares the computed digging depth and the depth set by the digging depth setting element 28. When the current digging depth exceeds a set depth, a command is generated to the boom cylinder 11 to expand the cylinder. This reduces the digging depth to prevent the ground from being excavated beyond the set depth.

In the bucket path control mode, operation command values are generated to each of the

cvlinders

11, 12, and 13 to correct the displacement between the desired path (linear digging path for maintaining the set depth) and the actual bucket position (computed based on the detected position of each of the

cylinders

11, 12, and 13). In other words, in the bucket path control mode, since linear control movement is performed on the bucket 10 irrespective of the digging load, automatic digging which is suitable for finish digging can be carried out.

Finally, the combined control mode will be described. In this control mode, rough digging is executed based on the aforementioned digging load control mode, and, during rough digging, the control section constantly judges whether or not the bucket 10 has reached the set height (1 meter above ground level in the embodiment) and whether or not the bucket 10 has equaled a depth set by the digging depth setting element 28. When height of the bucket 10 has been judged to equal the set height, the combined control mode is temporarily stopped upon judgment that the boom 8 has automatically moved upward when the bucket 10 has become full. When the bucket 10 has been judged to reach a set depth, the rough digging is completed and finish digging is executed. In addition, in the finish digging, when the arm cylinder 12 or the bucket cylinder 13 has reached the stroke end, or in other words when the bucket 10 has reached the place where digging is completed, a command is generated to the boom cylinder to expand it. This causes the boom 8 to move upward. When the height of the bucket 10 has equalled the set height, the combined control mode is temporarily stopped. On the other hand, when it has been judged that an overload has occurred before the bucket has reached the location where the digging is completed (comparison is made between a previously set overload value and the value detected by the digging load detecting sensor 23), the control section 7 judges whether or not the bucket 10 is located at the front side of the arm 9 at its vertical position. When it is judged that the bucket is not located at the front side, the digging depth at that time is temporarily substituted as the set depth. The finish digging (bucket path control mode) is continued based on the substituted set depth. On the other hand, when it is judged that the bucket 10 is located at the front side of the arm 9 at its vertical position, rough digging (digging load control mode, but the boom 8 is not moved downward) is performed again until height of the bucket 10 equals the set height. The flow chart shown in Fig. 5 illustrates the control procedure which is carried out each time automatic digging is performed. The procedure is repeatedly carried out assuming that earth removing operations such as automatic earth removal control and manual earth removal operation are to be performed.

In the embodiment of the present invention having such a construction, when the digging load control mode is selected to start automatic digging, variations in digging depth may result due to changes in the hardness of the ground and the presence of obstacles. In the digging load control mode, however, when operating

lever

22L or 22R is operated, the command values of the

cylinders

11, 12, and 13 which correspond to the lever operation direction are each adjusted depending on the lever operation input. This allows such things as the operation position and the operation speed of each of the

cylinders

11, 12, and 13 to be freely changed. This means that the variations in digging depth in automatic digging can be easily corrected by simply operating the operating

lever

22L or 22R, without canceling the special automatic digging control mode. As a result of this, operations for automatic digging can be carried out easily with considerably higher precision.

In the digging load control mode, when the current digging depth exceeds a set depth, an expansion command is generated to the boom cylinder 11 to make the digging depth shallower. At the same time, the digging load at this point is temporarily substituted as the set load. This prevents the digging depth from exceeding the set depth. Consequently, digging operations can be carried out with high precision and with high efficiency because too much earth will not be excavated which would require the additional operation of returning the excavated earth back to the ground.

The bucket path control mode is also provided in addition to the digging load control mode, in which mode the bucket 10 is controlled linearly along the aimed path. Therefore, after rough digging has been performed due to the digging load control mode, finish digging can be executed due to the bucket path control mode. As a result, digging operations can be carried out very efficiently and with high precision.

The combined control mode is also provided which allows the mode to be automatically switched from the aforementioned load control mode to the bucket path control mode when the digging depth has equaled a set depth, and the mode to automatically switch from the bucket path control mode to the digging load control mode when a digging overload has occurred. Therefore, digging can be carried out very precisely and very efficiently by repeating both control modes. In addition, digging operations can be carried out more easily because mode switching does not need to be carried out. Further, imprecise and inefficient digging operations which result from erroneous mode switching can be reliably prevented.

In sum, since the present invention is constructed as described above, it allows automatic digging to be carried out with the digging load maintained at a set load, while at the same time it allows corrections of the operation commands of each of the cylinders by lever operation during automatic digging. Accordingly, variations in the digging depth which occur during automatic digging can be easily corrected by simply operating levers, without the operator having to go through the trouble of canceling the automatic digging control mode. As a result, automatic digging operations can be carried out very easily with very high precision.

The depth limiting means, which is provided to prevent the digging depth, during automatic digging, from becoming greater than a set depth, markedly increases the digging precision because over-digging is prevented, and also the digging efficiency because too much earth will not be excavated which would require the additional operation of returning the excavated earth back to the ground.

When the digging load control means for maintaining the digging load during automatic digging at a set load and the bucket path control means for aligning the bucket path during automatic digging and a set path are both provided, after rough digging has been executed in the digging load control mode, finish digging can be executed due to the bucket path control mode. As a result, digging operations can be carried out very efficiently and with high precision.

When the control automatic switching means for automatically switching the mode from the digging load control mode to the bucket path control mode when the digging depth has equaled the set depth, or the control automatic switching means for automatically switching the mode from the bucket path control mode to the digging load control mode when a digging overload has occurred are provided, operations can be carried out very easily because control switching does not need to be carried out. Accordingly, since erroneous control switching is prevented, the problems of reduced digging precision and operation efficiency are overcome.

In addition, when both of the aforementioned control automatic switching means are provided, high precision digging can be performed very efficiently by repeating these two types of control operations.

Claims

An excavator control apparatus for construction equipment of the type which has a movable boom (8), an arm (9) pivotably coupled to the boom, a bucket (10) carried by the arm, an operating section (3, 4) rotatably coupled to the equipment body, and operating cylinders (11, 12, 13) for operating the boom, arm and bucket, said operating section comprising an automatic digging control section (7) which allows automatic digging by controlling the operation of each of said cylinders, and being characterised by

digging load control means (7, 23, 27) for detecting a digging load when a digging depth is shallower than a set digging depth during automatic digging and for generating operating commands for each of the cylinders (11, 12 13) so that the cylinders are operable to maintain said detected digging load at a set load;

bucket path control means (7, 14, 15, 16) for generating operating commands to each of the cylinders so that the cylinders are operated in such a way that the bucket is caused to follow a path, during automatic digging, which corresponds to a set path; and

control automatic switching means (7) for automatically switching between a digging load control mode and a bucket path control mode in accordance with predetermined conditions.
An excavator control apparatus according to claim 1, wherein automatic switching from a digging load control mode to a bucket path control mode is arranged to be done by detecting that a digging depth has reached a set digging depth.
An excavator control apparatus according to claim 1, wherein automatic switching from a bucket path control mode to a digging load control mode is arranged to be done when a digging overload has been detected.
An excavator control apparatus according to claim 1, wherein the control automatic switching means (7) includes first control automatic switching means (7) for automatically switching the mode from a digging load control mode to a bucket path control mode when a digging depth has reached a set digging depth, and second control automatic switching means (7) for automatically switching the mode from a bucket path control mode to a digging load control mode when a digging overload has been detected.
An excavator control apparatus according to any one of claims 1, 2 and 4 wherein said automatic digging control section further includes operation command correcting means (7) for correcting the operating commands for each of the cylinders based on the operation of a lever (22L, 22R) during automatic digging; and

depth limiting means for correcting the operating commands for each of the cylinders (11, 12, 13) so as to prevent a digging depth during automatic digging from becoming greater than a set digging depth.